There is a continuing need to improve the flame, heat and flash protection of pilots, firefighters, steelworkers, and the like. This is particularly critical for personnel who are frequently at close quarters when heat, flame and flash hazards occur. The primary line of protection is the fabric in the protective clothing worn by the individual. It is also important that this clothing feel comfortable and look good in order that it will be worn all the time that the individual would be at risk.
The currently used protective m and p-aramid fabrics can melt and cling to the skin during severe heat or flame excursion. Although polybenzimidazole (PBI) is a significant improvement over the aramid fibers, it still will slightly shrink and pull and is extremely expensive. The Navy Clothing and Textile Research Center has found that oxidized polyacrylonitrile fiber (OPF) offers the best heat, flame and flash protection of any textile fiber currently available. It is a good insulator, does not melt and can withstand temperatures up to 5500.degree. F. briefly without catastrophic failure.
However, OPF has one major disadvantage; the 100% fabrics made from this material are susceptible to abrasion. This lack of the necessary amount of abrasion resistance has prevented its use in military protective clothing.
Inherently, flame-retardant fibers are well-known to those skilled in the art. These fibers, known as matrix fibers, though useful because of their flame-retardant qualities, are not strong enough to form their own fabrics, tend to have a non-uniform composition, are not succeptible of being easily dyed, and, in general, are not alone suitable for production into piece goods from which finished products, like clothing, are formed. On the other hand, conventional natural and synthetic fibers (staple fibers) which are alone suitable for production into finished piece goods, are not inherently flame-retardant.
One known attempted solution to the problem of producing an inherently flame-retardant fabric has been to blend matrix and staple fibers in various proportions. However, conventional techniques for producing blended staple yarns such as disclosed in U.S. Pat. Nos. 3,067,471 and 3,176,351 have not been successfully employed to produce a flame-retardant composite yarn, as far as is known.
Another method for producing untreated flame-retardant fabrics comprise the steps of separately blowing and carding bundles of matrix and staple fibers and then combining the sliver formed during a common drawing step to produce a blended sliver having desired proportions of matrix and staple fibers. Yet another method of producing untreated flame-retardant fabrics, and the subject of the present invention, is to produce a woven fabric having the desired flame-retardant characteristics.
It is not sufficient that the fabric merely be flame resistant and possess abrasion resistance. To be completely acceptable, the fabric must also be lightweight, conformable, nonscratchy, durable in normal use, dyeable, etc. in order that the garment made therefrom will be sufficiently comfortable and aesthetically attractive.
"Intimate blend" means that the individual staple components are not preferentially segregated within any particular region of the blend, beyond the normal fluctuation in distribution expected on a purely statistical basis. The blend may be in the form of a bale, a sliver, a yarn, a nonwoven, woven, or knitted fabric, etc. The fabrics are preferably "lightweight", i.e., have a basis weight of 3-10 oz/yd.sup.2. Intimate blends of the required proportions of the desired staple components may be prepared by various conventional textile blending techniques, e.g., cofeeding tows of fibers to a staple cutter; opening and air-mixing staple bales; combining slivers of staple prior to drafting, etc.